The technical field of this invention is a seat occupant detection system for a vehicle.
Vehicle seat occupant detection systems are used to help decide whether or how to deploy an airbag in a crash event. At least one such system provides an occupant characteristic sensor in a vehicle seat member to determine the weight of a seat occupant. The determination is made by a programmed computer provided in an occupant detection system module, the computer having an input connection from a seat characteristic sensor such as a fluid pressure sensor connected to a fluid filled bladder on the seat pan under the bottom seat cushion member. The output signal from the sensor is compared with seat calibration data, typically including calibrated threshold values, to characterize a detected seat occupant.
The seat calibration data are initially determined in calibration tests of the occupant detection system, which includes the seat cushion member, bladder, sensor and occupant detection system module, and are typically stored in rewritable, non-volatile memory such as EEPROM in the occupant detection system module. Since seat cushion members are generally made of a synthetic foam material that can change its force or pressure transfer characteristics with age and/or environmental variables, the use of the rewritable, non-volatile memory allows updating of the seat calibration data during vehicle operation, service or recalibration. To ensure that the seat calibration data are not lost, the vehicle manufacturer may direct that the system be replaced only by a complete, calibrated system that includes seat cushion member, bladder, sensor and occupant detection system module storing seat calibration data for the replacement seat cushion member. In the case of failure of the occupant detection system module, replacement of the module by itself will result in stored seat calibration data for the wrong seat cushion member, which could render the occupant detection system unreliable. It is thus desirable to provide detection of such an occurrence so that a need for corrective action may be signalled.
In one aspect of the invention, a vehicle seat cushion has a transponder responsive to a transponder activating signal to generate an electromagnetic signal containing unique seat identification data. Sensing apparatus is responsive to a characteristic of the vehicle seat cushion to generate a seat characteristic signal thereof; and an occupant detection module is responsive to the seat characteristic signal to derive a seat occupant signal and has a dedicated memory location for seat identification data in a rewritable, non-volatile memory. The occupant detection module generates the transponder activating signal, receives and processes the electromagnetic signal to derive the seat identification data therefrom and compares the seat identification data from the electromagnetic signal with seat identification data in the dedicated memory location. If the seat identification data from the electromagnetic signal does not match the seat identification data in the dedicated memory location, the occupant detection module generates a warning signal and preferably prevents derivation of the seat occupant signal.
In another aspect of the invention, the occupant detection module further determines if there is seat identification data in the dedicated memory location and, if there is no seat identification data in the rewritable, non-volatile memory, copies the seat identification data from the electromagnetic signal to the dedicated memory location.
In yet another aspect of the invention, a vehicle seat cushion has a transponder responsive to a transponder activating signal to generate an electromagnetic signal containing unique seat identification data. Sensing apparatus is responsive to a characteristic of the vehicle seat cushion to generate a seat characteristic signal thereof; and an occupant detection module is responsive to the seat characteristic signal to derive a seat occupant signal and has a dedicated memory location for seat identification data in a rewritable, non-volatile memory. The occupant detection module further generates the transponder activating signal, receives and processes the electromagnetic signal to derive the seat identification data therefrom and determines if there is seat identification data in the dedicated memory location. If there is no seat identification data in the dedicated memory location, the occupant detection module further determines if the seat identification data from the electromagnetic signal matches seat identification data from a previously received electromagnetic signal and, if so, increments a count and stores the seat identification data from the electromagnetic signal as the seat identification data from a previously received electromagnetic signal. If the count exceeds a predetermined reference value, the seat identification data from the electromagnetic signal is copied to the dedicated memory location. But if there is seat identification data in the dedicated memory location, the occupant detection system module compares seat identification data from the electromagnetic signal with seat identification data in the dedicated memory location. If the seat identification data from the electromagnetic signal does not match the seat identification data in the dedicated memory location, the occupant detection module generates a warning signal and preferably prevents derivation of the seat occupant signal.